Abstract Detail

Systemic acquired resistance in moss: Further evidence for conserved defense mechanisms in plants.

Vascular plants possess multiple mechanisms for defending themselves against pathogens. One well-characterized defense mechanism is systemic acquired resistance (SAR), in which a plant detects the presence of a pathogen and transmits a signal throughout the plant, inducing changes in the expression of various pathogenesis-related (PR) genes. Once SAR is established, the plant is capable of mounting rapid responses to subsequent pathogen attacks. SAR has been characterized in numerous vascular plants; however, our understanding of the evolutionary history of SAR is incomplete since its presence in non-vascular plants has not been conclusively demonstrated. Previous studies have alluded to the presence of an SAR in moss, however, none of these have conclusively shown that the phenotype exists. Here, we show that the moss species Amblystegium serpens does initiate an SAR-like reaction upon inoculation with Pythium irregulare, a common soil-borne oomycete. Within 24 hours of a primary inoculation, moss plants grown in culture became completely resistant to infection following subsequent inoculation by the same pathogen. This increased resistance was a response to the pathogen itself and not to physical wounding. Treatment with b1,3 glucan, a structural component of oomycete cell walls, was equally effective at triggering SAR. Our results demonstrate for the first time that this important defense mechanism exists in a non-vascular plant, and, together with previous studies, suggests that SAR arose prior to the divergence of vascular and non-vascular plants